The present invention relates to an apparatus and method for continuously monitoring the amount of particulate contained in emissions which are sampled from a smoke stack and measured at a location outside of the stack.
Emissions from smoke stacks are monitored in order to determine the nature and quantity of the matter which is emitted into the atmosphere. Such emissions have been, and will most likely continue to be, the subject of significant government regulation. At present, particulate mass is the only regulated variable of stack emissions for which there is no true real-time measurement.
Emissions are sampled from the stack using a variety of well known devices, including probes, nozzles, and tubes which perform sampling according to standards established by the United States Environmental Protection Agency and the American National Standards Institute.
Once extracted from the stack flow, the emissions, which include particulate, are transported outside of the stack to a measuring device which determines the amount of particulate matter contained within the emissions. The transport pipe used to carry the emissions is important because during transport of the sample from the stack to the measuring device for analysis, there is deposition of the particulate contained with the emissions to the transport pipe as the result of gravitational, thermal diffusion, and turbulent losses. These depositional losses prevent the particulate matter from being analyzed by the measuring device leading to incomplete measurement of the amount of particulate contained within the emissions. The rate of gravitational, diffusional and turbulent deposition losses depends on such factors as the flow rate of the emissions through the pipe, particle size and the pipe geometry.
Complex calculations are required in order to predict the depositional losses of particulate matter. Software can be used to provide estimates on the amount of particle transmission and/or deposition for a range of particle diameters; however, on a real-time basis it is generally not possible to correct the amount of particulate matter transmitted through the system to take into account the losses. Any attempt to make such a correction leads to uncertainty in sampling results.
There is a variety of conventional devices that are used to estimate the mass of particulate matter in emissions which are expelled from a smoke stack.
One well-known apparatus is a light attenuation system that is based on the extinction of a light beam as it traverses the stack. Though this apparatus provides monitoring on a real-time basis, true mass correlation with light attenuation is not possible which can lead to inaccurate results.
A second apparatus involves obtaining actual mass data by a batch sampling technique with a retrospective analysis. In this apparatus, a probe is inserted into a stack at a number of different locations in order to extract a composite sample of the particulate matter. This sample is analyzed at a later time in order to determine the average of the mass of particulate emitted from the stack. The procedure involves washing the inside of the probe and transport line to recover wall losses. This batch sampling, which can provide accurate values of mass concentration, is not capable of real-time measurement of the particulate mass within emissions.
While conventional systems can either provide real-time data or mass emission data, they cannot provide both. For the foregoing reasons a need exists for an apparatus and method for extracting representative samples from a stack, and transporting the sample to a mass-monitoring device in order to continuously analyze the amount of particulate contained within the emissions without significant loss of particulate matter due to deposition.